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Ammonia transporter

March 17, 2024

Ammonia transporters (TC# 1.A.11) are structurally related membrane transport proteins called Amt proteins (ammonia transporters) in bacteria and plants, methylammonium/ammonium permeases (MEPs) in yeast, or Rhesus (Rh) proteins in chordates. In humans, the RhAG, RhBG, and RhCG Rhesus proteins constitute solute carrier family 42[2] whilst RhD and RhCE form the Rh blood group system. The three-dimensional structure of the ammonia transport protein AmtB from Escherichia coli has been determined by x-ray crystallography[3][4] revealing a hydrophobic ammonia channel.[5] The human RhCG ammonia transporter was found to have a similar ammonia-conducting channel structure.[1] It was proposed[citation needed] that the erythrocyte Rh complex is a heterotrimer of RhAG, RhD, and RhCE subunits in which RhD and RhCE might play roles in anchoring the ammonia-conducting RhAG subunit to the cytoskeleton. Based on reconstitution experiments, purified RhCG subunits alone can function to transport ammonia.[6] RhCG is required for normal acid excretion by the mouse kidney[7] and epididymis.[8]

Ammonia transporter
Human Rhesus C Glycoprotein. PDB 3hd6[1]
Identifiers
SymbolAmtB
PfamPF00909
InterProIPR001905
TCDB1.A.11
OPM superfamily13
OPM protein2ns1
Available protein structures:
Pfam  structures / ECOD  
PDBRCSB PDB; PDBe; PDBj
PDBsumstructure summary

Structure edit

The structure of the ammonia channel from E. coli,[3][4] was, at the time of its publication, the highest resolution structure of any integral membrane protein. It shows a trimer of subunits, each made up of 11 transmembrane segments (TMSs) and containing a pseudo two-fold symmetry.[9] Each monomer contains a hydrophobic ammonia conducting channel.

While prokaryotic ammonia channel proteins have an N-terminal region which acts as a signal sequence and is cleaved in the mature protein,[10] the Rhesus glycoproteins retain this as a 12th transmembrane helix in the mature protein.[1]

Substrate specificity edit

Most functionally characterized members of the family are ammonium uptake transporters.[11] Some, but not other Amt proteins also transport methylammonium.[12][13] Detailed phylogenetic analyses of plant homologues have been published.[14] In E. coli, NH4+, rather than NH3, may be the substrate of AmtB, but controversy still exists.[15][16][17] If NH4+ is transported, K+ possibly serves as a counter ion in an antiport process with K+, and that one histidine removes a proton off of NH4+ to yield NH3.[15]

Transport reaction edit

The generalized transport reaction catalyzed by members of the Amt family are suggested to be:

NH4+ (out) ⇌ NH4+ (in)

Mechanism edit

The X-ray structures have revealed that the pore of the Amt and Rh proteins is characterized by a hydrophobic portion about 12 Å long, in which electronic density was observed in the crystallographic study of AmtB from Escherichia coli. This electronic density was initially only observed when crystals were grown in the presence of ammonium, and was thus attributed to ammonia molecules. The Amt/Rh protein mechanism might involve the single-file diffusion of NH3 molecules. However, the pore could also be filled with water molecules. The possible presence of water molecules in the pore lumen calls for a reassessment of the notion that Amt/Rh proteins work as plain NH3 channels. Indeed, functional experiments on plant ammonium transporters and Rh proteins suggest a variety of permeation mechanisms including the passive diffusion of NH3, the antiport of NH4+/H+, the transport of NH4+, or the cotransport of NH3/H+. Lamoureux et al. discuss these mechanisms in light of functional and simulation studies on the AmtB transporter.[18]

Regulation edit

In E. coli the AmtB gene is expressed only under limiting nitrogen levels to yield the AmtB protein. It is co-expressed with the GlnK gene which encodes a PII protein. This protein is also trimeric and remains in the cytoplasm.[19] It is covalently modified by a U/U deuridylylated group at Y51. The hydrolyzed product, adenosine 5'-diphosphate, orients the surface of GlnK for AmtB blockade. When nitrogen levels outside the cell rise, the ammonia channel must be deactivated to prevent excessive ammonia entering the cell (where ammonia would be combined with glutamate to make glutamine, utilizing ATP and thereby depleting the cell's ATP reserves). This deactivation is achieved by deuridylylation of the GlnK protein which then binds to the cytoplasmic face of AmtB and inserts a loop into the ammonia conducting pore. At the tip of this loop is an arginine residue which sterically blocks the channel.[20]

Human ammonia transporter-related proteins edit

RHAG, RHBG, RHCE, RHCG, RHD

References edit

  1. ^ a b c Gruswitz, F.; Chaudhary, S.; Ho, J. D.; Schlessinger, A.; Pezeshki, B.; Ho, C. -M.; Sali, A.; Westhoff, C. M.; Stroud, R. M. (2010). "Function of human Rh based on structure of RhCG at 2.1 A". Proceedings of the National Academy of Sciences. 107 (21): 9638–9643. doi:10.1073/pnas.1003587107. PMC 2906887. PMID 20457942.
  2. ^ Nakhoul NL, Hamm LL (Feb 2004). "Non-erythroid Rh glycoproteins: a putative new family of mammalian ammonium transporters". Pflügers Archiv. 447 (5): 807–12. doi:10.1007/s00424-003-1142-8. PMID 12920597. S2CID 24601165.
  3. ^ a b 1xqe; Khademi S, O'Connell J, Remis J, Robles-Colmenares Y, Miercke LJ, Stroud RM (Sep 2004). "Mechanism of ammonia transport by Amt/MEP/Rh: structure of AmtB at 1.35 A". Science. 305 (5690): 1587–94. CiteSeerX 10.1.1.133.6480. doi:10.1126/science.1101952. PMID 15361618. S2CID 11436509.
  4. ^ a b 2u7c; Zheng L, Kostrewa D, Bernèche S, Winkler FK, Li XD (Dec 2004). "The mechanism of ammonia transport based on the crystal structure of AmtB of Escherichia coli". Proceedings of the National Academy of Sciences of the United States of America. 101 (49): 17090–5. Bibcode:2004PNAS..10117090Z. doi:10.1073/pnas.0406475101. PMC 535379. PMID 15563598.
  5. ^ Khademi S, Stroud RM (Dec 2006). "The Amt/MEP/Rh family: structure of AmtB and the mechanism of ammonia gas conduction". Physiology. 21 (6): 419–29. doi:10.1152/physiol.00051.2005. PMID 17119155.
  6. ^ Mouro-Chanteloup I, Cochet S, Chami M, Genetet S, Zidi-Yahiaoui N, Engel A, Colin Y, Bertrand O, Ripoche P (2010). Fatouros D (ed.). "Functional reconstitution into liposomes of purified human RhCG ammonia channel". PLOS ONE. 5 (1): e8921. Bibcode:2010PLoSO...5.8921M. doi:10.1371/journal.pone.0008921. PMC 2812482. PMID 20126667.
  7. ^ Wagner CA, Devuyst O, Belge H, Bourgeois S, Houillier P (Jan 2011). "The rhesus protein RhCG: a new perspective in ammonium transport and distal urinary acidification" (PDF). Kidney International. 79 (2): 154–61. doi:10.1038/ki.2010.386. PMID 20927037.
  8. ^ Biver S, Belge H, Bourgeois S, Van Vooren P, Nowik M, Scohy S, Houillier P, Szpirer J, Szpirer C, Wagner CA, Devuyst O, Marini AM (Nov 2008). "A role for Rhesus factor Rhcg in renal ammonium excretion and male fertility". Nature. 456 (7220): 339–43. Bibcode:2008Natur.456..339B. doi:10.1038/nature07518. PMID 19020613. S2CID 205215412.
  9. ^ Conroy MJ, Jamieson SJ, Blakey D, Kaufmann T, Engel A, Fotiadis D, Merrick M, Bullough PA (Dec 2004). "Electron and atomic force microscopy of the trimeric ammonium transporter AmtB". EMBO Reports. 5 (12): 1153–8. doi:10.1038/sj.embor.7400296. PMC 1299191. PMID 15568015.
  10. ^ Thornton J, Blakey D, Scanlon E, Merrick M (May 2006). "The ammonia channel protein AmtB from Escherichia coli is a polytopic membrane protein with a cleavable signal peptide". FEMS Microbiology Letters. 258 (1): 114–20. doi:10.1111/j.1574-6968.2006.00202.x. PMID 16630265.
  11. ^ Soupene, Eric; King, Natalie; Feild, Eithne; Liu, Phillip; Niyogi, Krishna K.; Huang, Cheng-Han; Kustu, Sydney (2002-05-28). "Rhesus expression in a green alga is regulated by CO(2)". Proceedings of the National Academy of Sciences of the United States of America. 99 (11): 7769–7773. Bibcode:2002PNAS...99.7769S. doi:10.1073/pnas.112225599. ISSN 0027-8424. PMC 124347. PMID 12032358.
  12. ^ Musa-Aziz, Raif; Chen, Li-Ming; Pelletier, Marc F.; Boron, Walter F. (2009-03-31). "Relative CO2/NH3 selectivities of AQP1, AQP4, AQP5, AmtB, and RhAG". Proceedings of the National Academy of Sciences of the United States of America. 106 (13): 5406–5411. Bibcode:2009PNAS..106.5406M. doi:10.1073/pnas.0813231106. ISSN 1091-6490. PMC 2664022. PMID 19273840.
  13. ^ Andrade, Susana L. A.; Einsle, Oliver (2007-12-01). "The Amt/Mep/Rh family of ammonium transport proteins". Molecular Membrane Biology. 24 (5–6): 357–365. doi:10.1080/09687680701388423. ISSN 0968-7688. PMID 17710640. S2CID 41937253.
  14. ^ von Wittgenstein, Neil J. J. B.; Le, Cuong H.; Hawkins, Barbara J.; Ehlting, Jürgen (2014-01-01). "Evolutionary classification of ammonium, nitrate, and peptide transporters in land plants". BMC Evolutionary Biology. 14: 11. doi:10.1186/1471-2148-14-11. ISSN 1471-2148. PMC 3922906. PMID 24438197.
  15. ^ a b Fong, Rebecca N.; Kim, Kwang-Seo; Yoshihara, Corinne; Inwood, William B.; Kustu, Sydney (2007-11-20). "The W148L substitution in the Escherichia coli ammonium channel AmtB increases flux and indicates that the substrate is an ion". Proceedings of the National Academy of Sciences of the United States of America. 104 (47): 18706–18711. Bibcode:2007PNAS..10418706F. doi:10.1073/pnas.0709267104. ISSN 1091-6490. PMC 2141841. PMID 17998534.
  16. ^ Ishikita, Hiroshi; Knapp, Ernst-Walter (2007-02-07). "Protonation states of ammonia/ammonium in the hydrophobic pore of ammonia transporter protein AmtB". Journal of the American Chemical Society. 129 (5): 1210–1215. doi:10.1021/ja066208n. ISSN 0002-7863. PMID 17263403.
  17. ^ Javelle, Arnaud; Lupo, Domenico; Zheng, Lei; Li, Xiao-Dan; Winkler, Fritz K.; Merrick, Mike (2006-12-22). "An unusual twin-his arrangement in the pore of ammonia channels is essential for substrate conductance". The Journal of Biological Chemistry. 281 (51): 39492–39498. doi:10.1074/jbc.M608325200. ISSN 0021-9258. PMID 17040913.
  18. ^ Lamoureux, G.; Javelle, A.; Baday, S.; Wang, S.; Bernèche, S. (2010-09-01). "Transport mechanisms in the ammonium transporter family". Transfusion Clinique et Biologique. 17 (3): 168–175. doi:10.1016/j.tracli.2010.06.004. ISSN 1953-8022. PMID 20674437.
  19. ^ Durand A, Merrick M (Oct 2006). "In vitro analysis of the Escherichia coli AmtB-GlnK complex reveals a stoichiometric interaction and sensitivity to ATP and 2-oxoglutarate". The Journal of Biological Chemistry. 281 (40): 29558–67. doi:10.1074/jbc.M602477200. PMID 16864585.
  20. ^ 2nuu; Conroy MJ, Durand A, Lupo D, Li XD, Bullough PA, Winkler FK, Merrick M (Jan 2007). "The crystal structure of the Escherichia coli AmtB-GlnK complex reveals how GlnK regulates the ammonia channel". Proceedings of the National Academy of Sciences of the United States of America. 104 (4): 1213–8. Bibcode:2007PNAS..104.1213C. doi:10.1073/pnas.0610348104. PMC 1783118. PMID 17220269.

As of this edit, this article uses content from "1.A.11 The Ammonium Channel Transporter (Amt) Family", which is licensed in a way that permits reuse under the Creative Commons Attribution-ShareAlike 3.0 Unported License, but not under the GFDL. All relevant terms must be followed.

March 17, 2024
ammonia, transporter, structurally, related, membrane, transport, proteins, called, proteins, ammonia, transporters, bacteria, plants, methylammonium, ammonium, permeases, meps, yeast, rhesus, proteins, chordates, humans, rhag, rhbg, rhcg, rhesus, proteins, co. Ammonia transporters TC 1 A 11 are structurally related membrane transport proteins called Amt proteins ammonia transporters in bacteria and plants methylammonium ammonium permeases MEPs in yeast or Rhesus Rh proteins in chordates In humans the RhAG RhBG and RhCG Rhesus proteins constitute solute carrier family 42 2 whilst RhD and RhCE form the Rh blood group system The three dimensional structure of the ammonia transport protein AmtB from Escherichia coli has been determined by x ray crystallography 3 4 revealing a hydrophobic ammonia channel 5 The human RhCG ammonia transporter was found to have a similar ammonia conducting channel structure 1 It was proposed citation needed that the erythrocyte Rh complex is a heterotrimer of RhAG RhD and RhCE subunits in which RhD and RhCE might play roles in anchoring the ammonia conducting RhAG subunit to the cytoskeleton Based on reconstitution experiments purified RhCG subunits alone can function to transport ammonia 6 RhCG is required for normal acid excretion by the mouse kidney 7 and epididymis 8 Ammonia transporterHuman Rhesus C Glycoprotein PDB 3hd6 1 IdentifiersSymbolAmtBPfamPF00909InterProIPR001905TCDB1 A 11OPM superfamily13OPM protein2ns1Available protein structures Pfam structures ECOD PDBRCSB PDB PDBe PDBjPDBsumstructure summary Contents 1 Structure 2 Substrate specificity 2 1 Transport reaction 3 Mechanism 4 Regulation 5 Human ammonia transporter related proteins 6 ReferencesStructure editThe structure of the ammonia channel from E coli 3 4 was at the time of its publication the highest resolution structure of any integral membrane protein It shows a trimer of subunits each made up of 11 transmembrane segments TMSs and containing a pseudo two fold symmetry 9 Each monomer contains a hydrophobic ammonia conducting channel While prokaryotic ammonia channel proteins have an N terminal region which acts as a signal sequence and is cleaved in the mature protein 10 the Rhesus glycoproteins retain this as a 12th transmembrane helix in the mature protein 1 Substrate specificity editMost functionally characterized members of the family are ammonium uptake transporters 11 Some but not other Amt proteins also transport methylammonium 12 13 Detailed phylogenetic analyses of plant homologues have been published 14 In E coli NH4 rather than NH3 may be the substrate of AmtB but controversy still exists 15 16 17 If NH4 is transported K possibly serves as a counter ion in an antiport process with K and that one histidine removes a proton off of NH4 to yield NH3 15 Transport reaction edit The generalized transport reaction catalyzed by members of the Amt family are suggested to be NH4 out NH4 in Mechanism editThe X ray structures have revealed that the pore of the Amt and Rh proteins is characterized by a hydrophobic portion about 12 A long in which electronic density was observed in the crystallographic study of AmtB from Escherichia coli This electronic density was initially only observed when crystals were grown in the presence of ammonium and was thus attributed to ammonia molecules The Amt Rh protein mechanism might involve the single file diffusion of NH3 molecules However the pore could also be filled with water molecules The possible presence of water molecules in the pore lumen calls for a reassessment of the notion that Amt Rh proteins work as plain NH3 channels Indeed functional experiments on plant ammonium transporters and Rh proteins suggest a variety of permeation mechanisms including the passive diffusion of NH3 the antiport of NH4 H the transport of NH4 or the cotransport of NH3 H Lamoureux et al discuss these mechanisms in light of functional and simulation studies on the AmtB transporter 18 Regulation editIn E coli the AmtB gene is expressed only under limiting nitrogen levels to yield the AmtB protein It is co expressed with the GlnK gene which encodes a PII protein This protein is also trimeric and remains in the cytoplasm 19 It is covalently modified by a U U deuridylylated group at Y51 The hydrolyzed product adenosine 5 diphosphate orients the surface of GlnK for AmtB blockade When nitrogen levels outside the cell rise the ammonia channel must be deactivated to prevent excessive ammonia entering the cell where ammonia would be combined with glutamate to make glutamine utilizing ATP and thereby depleting the cell s ATP reserves This deactivation is achieved by deuridylylation of the GlnK protein which then binds to the cytoplasmic face of AmtB and inserts a loop into the ammonia conducting pore At the tip of this loop is an arginine residue which sterically blocks the channel 20 Human ammonia transporter related proteins editRHAG RHBG RHCE RHCG RHDReferences edit a b c Gruswitz F Chaudhary S Ho J D Schlessinger A Pezeshki B Ho C M Sali A Westhoff C M Stroud R M 2010 Function of human Rh based on structure of RhCG at 2 1 A Proceedings of the National Academy of Sciences 107 21 9638 9643 doi 10 1073 pnas 1003587107 PMC 2906887 PMID 20457942 Nakhoul NL Hamm LL Feb 2004 Non erythroid Rh glycoproteins a putative new family of mammalian ammonium transporters Pflugers Archiv 447 5 807 12 doi 10 1007 s00424 003 1142 8 PMID 12920597 S2CID 24601165 a b 1xqe Khademi S O Connell J Remis J Robles Colmenares Y Miercke LJ Stroud RM Sep 2004 Mechanism of ammonia transport by Amt MEP Rh structure of AmtB at 1 35 A Science 305 5690 1587 94 CiteSeerX 10 1 1 133 6480 doi 10 1126 science 1101952 PMID 15361618 S2CID 11436509 a b 2u7c Zheng L Kostrewa D Berneche S Winkler FK Li XD Dec 2004 The mechanism of ammonia transport based on the crystal structure of AmtB of Escherichia coli Proceedings of the National Academy of Sciences of the United States of America 101 49 17090 5 Bibcode 2004PNAS 10117090Z doi 10 1073 pnas 0406475101 PMC 535379 PMID 15563598 Khademi S Stroud RM Dec 2006 The Amt MEP Rh family structure of AmtB and the mechanism of ammonia gas conduction Physiology 21 6 419 29 doi 10 1152 physiol 00051 2005 PMID 17119155 Mouro Chanteloup I Cochet S Chami M Genetet S Zidi Yahiaoui N Engel A Colin Y Bertrand O Ripoche P 2010 Fatouros D ed Functional reconstitution into liposomes of purified human RhCG ammonia channel PLOS ONE 5 1 e8921 Bibcode 2010PLoSO 5 8921M doi 10 1371 journal pone 0008921 PMC 2812482 PMID 20126667 Wagner CA Devuyst O Belge H Bourgeois S Houillier P Jan 2011 The rhesus protein RhCG a new perspective in ammonium transport and distal urinary acidification PDF Kidney International 79 2 154 61 doi 10 1038 ki 2010 386 PMID 20927037 Biver S Belge H Bourgeois S Van Vooren P Nowik M Scohy S Houillier P Szpirer J Szpirer C Wagner CA Devuyst O Marini AM Nov 2008 A role for Rhesus factor Rhcg in renal ammonium excretion and male fertility Nature 456 7220 339 43 Bibcode 2008Natur 456 339B doi 10 1038 nature07518 PMID 19020613 S2CID 205215412 Conroy MJ Jamieson SJ Blakey D Kaufmann T Engel A Fotiadis D Merrick M Bullough PA Dec 2004 Electron and atomic force microscopy of the trimeric ammonium transporter AmtB EMBO Reports 5 12 1153 8 doi 10 1038 sj embor 7400296 PMC 1299191 PMID 15568015 Thornton J Blakey D Scanlon E Merrick M May 2006 The ammonia channel protein AmtB from Escherichia coli is a polytopic membrane protein with a cleavable signal peptide FEMS Microbiology Letters 258 1 114 20 doi 10 1111 j 1574 6968 2006 00202 x PMID 16630265 Soupene Eric King Natalie Feild Eithne Liu Phillip Niyogi Krishna K Huang Cheng Han Kustu Sydney 2002 05 28 Rhesus expression in a green alga is regulated by CO 2 Proceedings of the National Academy of Sciences of the United States of America 99 11 7769 7773 Bibcode 2002PNAS 99 7769S doi 10 1073 pnas 112225599 ISSN 0027 8424 PMC 124347 PMID 12032358 Musa Aziz Raif Chen Li Ming Pelletier Marc F Boron Walter F 2009 03 31 Relative CO2 NH3 selectivities of AQP1 AQP4 AQP5 AmtB and RhAG Proceedings of the National Academy of Sciences of the United States of America 106 13 5406 5411 Bibcode 2009PNAS 106 5406M doi 10 1073 pnas 0813231106 ISSN 1091 6490 PMC 2664022 PMID 19273840 Andrade Susana L A Einsle Oliver 2007 12 01 The Amt Mep Rh family of ammonium transport proteins Molecular Membrane Biology 24 5 6 357 365 doi 10 1080 09687680701388423 ISSN 0968 7688 PMID 17710640 S2CID 41937253 von Wittgenstein Neil J J B Le Cuong H Hawkins Barbara J Ehlting Jurgen 2014 01 01 Evolutionary classification of ammonium nitrate and peptide transporters in land plants BMC Evolutionary Biology 14 11 doi 10 1186 1471 2148 14 11 ISSN 1471 2148 PMC 3922906 PMID 24438197 a b Fong Rebecca N Kim Kwang Seo Yoshihara Corinne Inwood William B Kustu Sydney 2007 11 20 The W148L substitution in the Escherichia coli ammonium channel AmtB increases flux and indicates that the substrate is an ion Proceedings of the National Academy of Sciences of the United States of America 104 47 18706 18711 Bibcode 2007PNAS 10418706F doi 10 1073 pnas 0709267104 ISSN 1091 6490 PMC 2141841 PMID 17998534 Ishikita Hiroshi Knapp Ernst Walter 2007 02 07 Protonation states of ammonia ammonium in the hydrophobic pore of ammonia transporter protein AmtB Journal of the American Chemical Society 129 5 1210 1215 doi 10 1021 ja066208n ISSN 0002 7863 PMID 17263403 Javelle Arnaud Lupo Domenico Zheng Lei Li Xiao Dan Winkler Fritz K Merrick Mike 2006 12 22 An unusual twin his arrangement in the pore of ammonia channels is essential for substrate conductance The Journal of Biological Chemistry 281 51 39492 39498 doi 10 1074 jbc M608325200 ISSN 0021 9258 PMID 17040913 Lamoureux G Javelle A Baday S Wang S Berneche S 2010 09 01 Transport mechanisms in the ammonium transporter family Transfusion Clinique et Biologique 17 3 168 175 doi 10 1016 j tracli 2010 06 004 ISSN 1953 8022 PMID 20674437 Durand A Merrick M Oct 2006 In vitro analysis of the Escherichia coli AmtB GlnK complex reveals a stoichiometric interaction and sensitivity to ATP and 2 oxoglutarate The Journal of Biological Chemistry 281 40 29558 67 doi 10 1074 jbc M602477200 PMID 16864585 2nuu Conroy MJ Durand A Lupo D Li XD Bullough PA Winkler FK Merrick M Jan 2007 The crystal structure of the Escherichia coli AmtB GlnK complex reveals how GlnK regulates the ammonia channel Proceedings of the National Academy of Sciences of the United States of America 104 4 1213 8 Bibcode 2007PNAS 104 1213C doi 10 1073 pnas 0610348104 PMC 1783118 PMID 17220269 As of this edit this article uses content from 1 A 11 The Ammonium Channel Transporter Amt Family which is licensed in a way that permits reuse under the Creative Commons Attribution ShareAlike 3 0 Unported License but not under the GFDL All relevant terms must be followed Retrieved from https en wikipedia org w index php title Ammonia transporter amp oldid 1187810845, wikipedia, wiki, book, books, library,

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